Metal fractionation in marine sediments acidified by enrichment of CO2: A risk assessment

Carbon-capture and storage is considered to be a potential mitigation option for climate change. However, accidental leaks of CO2 can occur, resulting in changes in ocean chemistry such as acidification and metal mobilization. Laboratory experiments were performed to provide data on the effects of CO2-related acidification on the chemical fractionation of metal(loid)s in marine-contaminated sediments using sequential extraction procedures. The results showed that sediments from Huelva estuary registered concentrations of arsenic, copper, lead, and zinc that surpass the probable biological effect level established by international protocols. Zinc had the greatest proportion in the most mobile fraction of the sediment. Metals in this fraction represent an environmental risk because they are weakly bound to sediment, and therefore more likely to migrate to the water column. Indeed, the concentration of this metal was lower in the most acidified scenarios when compared to control pH, indicating probable zinc mobilization from the sediment to the seawater. •Acidification related to CO2 leakages modifies the geochemistry of metals.•Mobilization of metals from sediment into the water column is associated with their speciation.•Sediments from Huelva Estuary have relevant concentrations of As, Cu, Pb and Zn.•Risk assessment code analysis revealed that Zn presents the highest potential risk.